Capillary dried blood spot (DBS) samples facilitate field-based collection without venipuncture. This pilot study aims to evaluate the viability of creatine (Cr) and creatinine (Crt) quantification using fresh capillary serum (Cr
S
/Crt
S
) and DBS samples (Cr
DBS
/Crt
DBS
), using Flow Injection Analysis Mass Spectrometry (FIA – MS). Nine Olympic Athletes provided a capillary blood sample to assess Cr
S
/Crt
S
and Cr
DBS
/Crt
DBS
quantified by FIA – MS. No difference between Crt
S
(mean ± SD: 813.6 ± 102.4 μmol/L) and Crt
DBS
(812.4 ± 108.1
μ
mol/L) was observed with acceptable variance [SEM 88.7; CV 10.7%; ICC 0.57 (CI 95% 0.06 – 0.84)] and agreement [very strong (Spearman:
r
= 0.77;
p
< 0.01) or strong (Pearson:
r
= 0.56;
p
= 0.04); Bland Altman: lower (-193) and upper (+196) limits of agreement]. Cr
S
(mean ± SD: 691.8 ± 165.2
μ
mol/L) was significantly different to Cr
DBS
(2911 ± 571.4
μ
mol/L) with unacceptable variance [SEM 171.6; CV 27%; ICC 0.002 (CI 95% -0.02 – 0.07)] and ‘weak’ agreement [Spearman:
r
= 0.21,
p
= 0.47 and Pearson:
r
= 0.06,
p
= 0.84; Bland Altman lower (-3367) and upper (-1072) limits of agreement]. Crt quantification is viable using both Crt
S
and Crt
DBS
(but not for Cr and Cr
S
/Cr
DBS
), with the DBS tissue handling technique offering several methodological and practice facing advantages. Future work should expand upon the sample size, explore sport/discipline relevant analytes across a full competitive season, including key training, recovery and performance blocks of their periodized performance plan.